1. Field of the Invention
The present invention relates to a fuel injection control method of an engine, and a fuel injection control device for carrying out the same and in particular, relates to a fuel injection control method of an engine which determines a fuel injection time by a predetermined calculating method on the basis of detected data, to thereby enable maintaining of a targeted engine rotating speed, and a fuel injection control device for executing the method.
2. Description of the Related Art
In the fuel injection control of an engine such as a multipurpose engine having a comparatively small and simple construction, it is usual that the fuel injection time is determined by reading map data of an intake air flow rate experimentally obtained in advance on the basis of the values of an engine rotating speed, an intake pipe pressure and so on. However, since there is no constant correlation among these detected values, it is indispensable to store a correction quantity for each parameter as a map in a memory. Further, since there are many nonlinear elements which are incorporated in an engine system, it is practically difficult to exactly execute a fuel injection control and an engine rotating speed control using the map in the described manner.
Taking the above situation into consideration, the inventors of the present application previously proposed, in Japanese Patent Application Laid-Open No. 2005-140063, a method of estimating the intake air flow rate by a predetermined calculation formula on the basis of an engine rotating speed and an intake pipe pressure, without using any map, and of determining a fuel injection time from the intake air flow rate to execute a fuel injection control. In addition to these data, a measure for estimating a more precise intake air flow rate by using data on an intake air temperature is also known.
That is to say, by deriving a predetermined formula on the basis of a given experimental verification about the physical relationship between the engine rotating speed and the intake pipe pressure, it is possible to execute control of the air-fuel ratio and an engine rotating speed while sequentially estimating the intake air flow rate. However, the control of the intake air flow rate at this case is performed by an electronic governor which controls opening and closing of a throttle valve. Hence, the fuel injection control must be delayed in time in comparison with the control that the electronic governor conducts, since a fuel injection time is determined by a negative pressure (an intake pipe pressure) generated by an intake air supplied to a downstream side of the throttle valve, and a target engine rotating speed.
Therefore, during s transient operation of an engine where an intake air flow rate and intake of fuel changes every moment, the control of the fuel injection quantity is delayed from the control of the intake air flow rate and therefore, may provide an adverse effect on the response to the target engine rotating speed. As a result, there is a problem such that it takes a long time for the engine rotating speed to converge into a target rotating speed, and an engine operability might be impaired.